This invention relates to a generator for generating an electric voltage, comprising a transformer having a core of ferromagnetic material, a primary winding and a secondary winding, the primary winding comprising a first primary coil wound in the form of a solenoid, said primary winding being connected to a primary circuit which comprises a source of time-dependent voltages, the secondary winding comprising a first secondary coil wound in the form of a solenoid and being connected to a secondary circuit, which first primary and secondary coils are concentrically disposed on the core with intermediate electrical insulation means.
The invention also relates to a transformer suitable for such a generator.
A generator of this kind is known from DE-B 2 626 285, which corresponds to U.S. Pat. No. 4,089,049 (May, 19, 1978). From this document it is also known that interference from the secondary circuit can reach the input terminals of the primary circuit via the capacitance existing between the primary and secondary windings. Such interference may have adverse effects on other circuits. Conversely, interference from the primary circuit can also reach the secondary circuit and a load connected thereto. The transfer of such interference is counteracted in the known generator by using electrostatic shields between the primary and secondary windings. Even though this method leads to the desired result, it also has a number of drawbacks. The introduction of the shields increases the cost of the transformer and its dimensions and weight also become greater. The coupling factor between the windings becomes smaller and hence the leakage inductance increases. Consequently, part of the energy is not transformed from the primary to the secondary side of the transformer. In order to protect the primary circuit, this energy must be dissipated, for example, in resistance networks. A small but not insignificant part of the power to be transferred may thus be lost.
NL-A-87 02 133, which corresponds to U.S. application Ser. No. 239,575 filed Sept. 1, 1988, describes a transformer in which an interference voltage between a primary and a secondary reference point is suppressed without utilizing electrostatic shields. To achieve this, the primary winding comprises a first and a second primary coil across which the voltage drop amounts to U.sub.1p and U.sub.2p, respectively, in the operating condition and which are capacitively coupled to a first and a second secondary coil, respectively, across which the voltage drop amounts to U.sub.1s and U.sub.2s, respectively, in the operating condition. The coupling capacitances amount to C.sub.1p and C.sub.2p, respectively. The object is achieved in that the following condition is satisfied: EQU C.sub.1 (U.sub.1s -U.sub.1p)=C.sub.2 (U.sub.2p -U.sub.2s).
In order to satisfy this condition, the properties of the insulation means and the number of turns of the primary and secondary coils must be carefully selected. Consequently, the construction of the transformer is comparatively complex and expensive.